There is acoustic cavity resonance produced by vibration of air with which the cavity of a tire is charged, which is one of the sources that create tire noise. The tread of a tire, which comes into contact with a road surface during running of a vehicle, vibrates due to unevenness of the road surface, and this vibration then causes the vibration of air in the cavity of the tire, thereby producing the cavity resonance. It is known that the frequency of sound caught as noise in the cavity resonance is generally about 200 Hz to 300 Hz, differing according to tire sizes. It is thus important to decrease the level of noise in this frequency band in order to reduce tire noise.
As an approach for reducing noise created by such acoustic cavity resonance, it has been proposed to add a sound absorbing member in the cavity of a tire to absorb the resonance sound (see Unexamined Japanese Patent Application Publication No. 62-216803, for example). However, in the case where the sound absorbing member is mounted on the inner surface of a tire with an adhesive or the like, because the member different from the tire is added inside the tire, stress is concentrated on the adhesive interface due to deformation of the tire during rotation of the tire, which often separates the sound absorbing member. Accordingly, there remain a lot of problems associated with how to mount the sound absorbing member thereon.
Attempts have been made to reduce the cavity resonance sound by constantly varying the frequency of resonance with revolving of a wheel by changing the cross-sectional shape of the cavity of a tire circumferentially of the tire. However, these attempts cause deterioration of mounting of the tire on a rim, or need modifications to production facilities or the like to a large extent because the structure of the tire or rim is modified.